Vacuum tube circuit



DeC. 25, 1934. 5 RUBEN VACUUM TUBE C IRCUIT Filed Dec. 10,- 1931 FIG.1.

INVENTOR- M BY HIS ATTORNEY- Patented Dec. 25, 1934 UNITED STATES PATENTOFFICE 6 Claims.

elements and to the connections of their elements in an electricalcircuit. It is an improvement upon the arrangement described in myUnited States Letters Patent 1,815,931, the improvement morespecifically being in respect to the structure of the tube and to themethod of obtaining grid bias potentials. The object of this inventionis the provision of a vacuum tube having high sensitivity and high poweroutput, also means for obtaining grid biasing without the use of anextra source of potential for this purpose.

Broadly, the invention consists of a vacuum tube employing plural setsof elements, preferably in parallel arrangement, one set being connectedto the input circuit and another to the output circuit and sointerconnected that the latter produces an amplified response to theenergy applied to the input electrodes of the first or controlling setof elements, the grids of the two sets having a predeterminedinter-relationship in respect to the number of turns of each and thespace separating them from their respective cathode elements. With acertain critical relationship established, maxima in sensitivity andpower output are reached. By means of the arrangement of these sets ofelements, high current amplification is efiected through the control ofthe electron discharge to the anode of one set of elements by thecathode-anode discharge in the other or control set of elements, and bythe parallel arrangement of the sets of elements, inter-element currentleakage is minimized.

My patent describes a tube in which there is a direct internalconnection between the cathode of the input set of elements and the gridof the output set of elements. By the terms of this invention thisconnection is external to the tube and the grid biasing potential isobtained directly from the plate current supply circuit instead of froma separate source of potential.

This tube utilizes the current changes produced in the plate circuit ofone set of elements when its grid is positively biased by the outputcurrent of the plate circuit of another set of elements; that is, bythat set of elements to the grid of which the input or controllingpotential is applied.

As set forth in my said patent, for a maximum output, the fundamentalrequirement is that the amplification factor of the controlling set ofelements to which the input potential is applied,

elements, the grid of which is normally positively biased by the platecurrent 01 the control set of elements, so that the device operates bychanges of positive bias potential or by the plate current changes inthe first or controlling set of elements. For this the impedance of theplate circuit of the controlling set of elements should bear a definiteratio to that of the input grid and cathode impedance of the output setof elements. To secure this arrangement the grid of the controlling setof elements is preferably placed more closely to itscathode than theother grid to its cathode, also having a greater number of turns thanthe grid of the other set of elements. For such maximum power output andpower sensitivity the product of the number of turns of the grid of thecontrol set of elements about its adjacent cathode and the diameter ofthe grid coil is preferably in a substantially fixed ratio to theproduct of the number of turns of the grid of the second set and thediameter of that grid coil, as more deflnitely indicated below.

In a practicable combination of elements in tubes of the commercial typecapable of having a transconductance of 25,000 microhms, after wideexperimentation in varying the grids in respect to their diameters andnumber of turns, when using nickel cathode tubes of 0.065" diametercoated with barium-strontium oxide, and tungsten heater wire, 0.006" indiameter, coated with aluminum oxide by an oxychloride reaction, thebest results were obtained with .0045 molybdenum wire grids of thefollowing specifications:

Input setcoil diameter 0.110"; turns 56 per inch of cathode length.

Output set-coil diameter 0.150"; turns 40 per inch of cathode length.

It will be noted that the product of grid turns per inch and thediameter of the coil for a tube of maximum sensitivity is about the samefor both input and output sets of elements. The anodes were made up ofplates of carbonized nickel 1" long in 3%" cylinders; the electricaldimensions being five volts and 1.75 amperes heater power, the platepotential 250 volts; positive bias output grid control current 4milliamperes--normal output plate current thirty milliamperes; negativecontrol grid bias voltage 5. Undistorted watt output is 2.5. Thenegative potential to reduce the normal output plate current twentyvolts is applied through a 20,000 ohm resistance. This is varied withthe use to which the tube is to be applied.

The amplification characteristics of the combination are especiallysuitable for the operation of relays by direct current potential becauseof the wide plate current changes occurring with small input gridpotential variations.

A plate current change caused, for instance, by a change of the inputpotential of the control grid, produces a change in the positivepotential applied to the normally positively biased output grid element;it causes a large reduction in the space charge of the output circuitand a plate current change in the output circuit. Thus, a variation ofone volt in the potential of the input grid gives a twenty-fivemilliampere change in the output plate circuit. The geometrical relationof the grids in their respective sets of elements, to afford the mostefficient combination of elements, is described specifically in respectto a tube containing two sets of elements; but this relation between thecontrol elements also holds in respect to the combination in which thesets of elements are in separate tubes as shown in my prior andcopending application bearing Serial Number 553,052, filed July 25,1931.

In some instances where separate and insulated sources of potential areavailable the cathodes may be directly and independently heated insteadof by indirect means as here indicated, and they may be of the filamenttype.

By my improved arrangement, to obtain the necessary bias potential ofthe grid of the input set or group of elements, a resistance isconnected in series with the cathode of that set and the grid of theoutput set of elements, and a condenser is shunted across it. And thereturn lead from the grid of the input set, for example from atransformer, is connected to the output grid and series resistancesinstead of with the cathode as shown in the patent. By this means anegative grid bias potential is obtained without the use of a separatesource of direct current potential which is an important factor in thedesign of a vacuum tube circuit to be operated by a commercial lightingcurrent.

By this arrangement also another negative bias is applied to the outputgrid which serves to reduce the output plate current when the controlplate current is reduced to a negligible amount. This output gridpotential is obtained by inserting in series with the cathode of theoutput set of elements a fixed resistance and condenser. The potentialdrop is applied by means of a series resistance to the grid element ofthe control grid. The efiect of this negative potential is had only whenthe potential drop between the cathode and grid elements, due to theplate current in the control grid, is less than the series resistancedrop of potential. Thus, the unbiased plate current of the output tubeis reduced to a lower value. When the plate current in the control tuberises, the bias potential is overcome and the output plate currentrises, and there is a more efllcient operation, with a material increasein the range of operation in terms of power output and the normal outputplate current required.

The invention is illustrated in the accompany ing drawing, in which 7Fig. 1 is a circuit diagram showing a complete network for practicingthe invention including a vacuum tube employing plural sets of elements.

Fig. 2 is a cross-sectional view of the tube structure.

For a better understanding of the invention reference is made to theaccompanying drawing of one embodiment therof.

Referring to Fig. 1, the cathode 1, grid 2 and plate 3 are the controlor input set of elements,

having leads at 5, 6 and '7 respectively. The cathode is, grid 2. andplate 3a are the output set of elements having leads at 5a, 6a and 78respectively. The insulated wire heater elements are 4. and 4a supportedon leads 8 and 8B. respectively. The glass spreader 9 assists insupporting both sets of elements so as to avoid vibration eflects.Connected between cathode 1 and grid 2a is resistance 14 which isshunted by condenser C. The input device such as transformer 1011, isconnected to input grid 2 and resistance 12, grid 2a being connected soas to be negatively biased. The drop of potential is due to resistance13 shunted by C1 in series with output cathode 19.. The resistancecauses the drop of potential across it which is applied through a seriesresistance 12, of 20,000 ohms, which negative potential reduces thenormal positive potential obtained from the input plate current set andnegatively biases the output grid only when the plate current of thecontrol set of elements is of very low value or at zero.

The translating device 15, such as aloud speaker, is connected in theoutput plate circuit. The potential for operating the elements isobtained from any of the commonly applied sources of sup- .ply, such asthe combination wherein tube 1'7,

with cathode and anodes 18 and 19, is the rectifier, C2 and C3 thefilter circuit condensers, and 16 the necessary inductance. Thetransformer, with various secondary windings 21, 22 and 23, supplies thenecessary cathode heating and plate potentials.

The method of obtaining the various grid bias potentials and theconnection of the element,

while shown in a single tube arrangement, is also applicable where theinput and output elements are in separate tubes as shown in myco-pending application bearing Serial Number 553,052 filed July 25,1931.

What I claim is:

1. In a vacuum tube circuit an electrical discharge device comprising anevacuated envelope containing a cathode, a grid and a plate element,another cathode insulated from the first mentioned cathode, grid andplate element insulated from the first mentioned plate element, saidsecond mentioned grid being connected with the first mentioned cathodethrough a series resistance element.

2. In a vacuum tube circuit, an electrical discharge device comprisingan evacuated envelope containing a cathode, a grid and a plate element,another cathode insulated from the first mentioned cathode, grid andplate element insulated from the first mentioned plate element, thefirst mentioned set of elements being mounted in a position parallel tothe second mentioned set of elements, the cathode of the first mentionedset of elements being connected to the grid of the second mentioned setof elements through a resistance element, so as to be at a potentialdifference with said grid.

3. In a vacuum tube circuit, an electrical discharge device comprisingan evacuated envelope containing an input set of elements consisting ofa cathode, a grid, an anode and a heater for heating the cathode, and anoutput set of elements consisting of a cathode insulated from the firstmentioned cathode, a grid and an anode insulated from the firstmentioned anode and a. heater for heating the cathode, the two sets ofelements being mounted in parallel positions and the output grid beingelectrically connected with the input cathode through a series connectedresistance.

4. In avacuum tube circuit an electrical discharge device comprising anevacuated envelope containing a triode consisting of a cathode, a gridand an anode and another triode consisting of a cathode, a grid and ananode, the cathodes being insulated from each other and the anodes beinginsulated from each other, the grid in the second mentioned triode beingconnected with the cathode in the first mentioned triode through aseries resistance, the amplification factor of one triode being higherthan the amplification factor of the other triode.

5. In a vacuum tube circuit an electrical discharge device comprising anevacuated envelope containing a triode consisting of a cathode, a gridand an anode, and another triode consisting of a cathode, a grid and ananode, the cathodes being insulated from each other and the anodes beinginsulated from each other, the grid in the second mentioned triode beingconnected with the oathode in the first mentioned triode through aseries resistance, the grid of the control triode having a greaternumber of turns and being closer to its cathode than the grid of theother triode in respect to its cathode.

6. In a vacuum tube circuit an electrical discharge device comprising anevacuated envelope containing a triode consisting of a cathode, a gridand an anode, and another triode consisting of a cathode, a grid and ananode, the cathodes being insulated from each other and the anodes beinginsulated from each other, the cathode in the first mentioned triodebeing connected through a resistance element with the grid 0! the secondmentioned triode, the grid of the control triode having a greater numberof turns than, and being closer to its cathode than the other grid, theproduct of the number of turns of wire 0! the control grid per unitlength of its cathode multiplied by the grid diameter beingsubstantially the equivalent of the product of the number of turns ofthe other grid multiplied by its diameter, the number of turns beingless than the number of turns of the 20 control grid.

SAMUEL RUBEN.

